A SLAG DEFOAMING COMPOSITE

Abstract: A slag defoaming composite, comprising a carbon source, a source of exothermic material, such as aluminium, and a dense inert granular material, such as calcium silicate. A binder is also optionally provided. The composite is preferably in briquette or pellet form, and is selected to have a density sufficient to penetrate the slag layer during processing.

Description: A SLAG DEFOAMING COMPOSITE BACKGROUND OF THE INVENTION This invention relates to a slag defoaming composite for example, for use in steel manufacture, which may preferably be in briquette or pellet form. However, the invention is not restricted to steel manufacture and may be suitable in a number of applications where the defoaming of slag or the reduction of oxides to the metallic state is required. During steel manufacture, iron from a blast furnace is converted to steel by placing the iron in a basic oxygen furnace. The quantity of iron can vary. Typically, it is about 200 tonnes. Oxygen is blown into the iron by an oxygen lance and the removal of impurities such as carbon, silicon, manganese, etc., converts the iron to steel. During the blowing process the slag on top of the steel foams to varying degrees dependent on the type of steel being produced. This foaming of the slag is undesirable as it extends the steel making time and therefore results in additional energy and labour costs. It is known that elements such as carbon or aluminium exothermically react with slag, thereby raising the temperature of the slag, reducing viscosity and allowing gases such as carbon monoxide and carbon dioxide to be released from this more fluid liquid and hence reduce or stop the foaming action. In the past products, such as tightly wound newspaper, timber, oil or tar derivatives, waste paper pulp, aluminium powder and pure aluminium metal, have been added to the slag in order to reduce foaming. A number of disadvantages are associated with such known defoaming products. Firstly, the low density of some of these products does not allow them to penetrate the slag, and hence the defoaming action is inefficient. Secondly, when utilising ύh'- defoaming additives the material is stored in a hopper above the blast furnace where conditions are hot, and sparks and lime dust are present. Under such conditions a number of the known defoaming additives can spontaneously combust either because of their carbonacious content or because of lime powder settling on the product, becoming moist and reacting exothermically with the product. SUMMARY OF THE INVENTION The present invention seeks to ameliorate the abovementioned disadvantages and provide an efficient and rapid defoaming agent. In one broad form, the present invention provides a slag defoaming composite, comprising: a carbon source; a source of exothermic material, such as aluminium; a dense insert granular material, such as calcium alumina silicate; and a binder, optionally provided; characterised in that, said composite is selected to have a density sufficient to penetrate the slag layer during processing. Most preferably, said composite is manufactured in the form of briquettes pellets, and/or the like. In a preferred embodiment, said slag defoaming composite is substantially non-combustible. Perhaps most preferably, the density of said composite is selected to be in the range of 1.0 to 2.6 g/cc. In a preferred form of the invention, the slag defoaming composite comprises: a carbon source which yields a final carbon content cf the composite in the range of 3 to 50% w/w; a source of aluminium which yields a final aluminium content of the composite within the range of 5 to 60% w/w; a calcium alumino silicate or a similar dense inert granular material within the range of 10 to 50% w/w; and a binder within the range of 0 to 20% w/w. Most preferably, said binder is sodium silicate or similar silicate derivatives, be they organic or inorganic, or clay, lime, or the like. Preferably, the composite further comprises a lubricant material. Most preferably, said lubricant material is a stearate, such as calcium stearate. Preferably, said lubricant material is provided within the range of 0 to 2% w/w. Preferably, said composite further comprises a slag fluidiser. Most preferably, said slag fluidiser is provided in the range of 0 to 30% w/w. In another form, the composite further comprises: cellulose based raw material; and flame retardent. Preferably, said cellulose based raw material is provided in the range of 3 to 30% w/w. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The slag defoaming composite of the present invention, and the process to manufacture same in briquette form, will now be described by way of example, describing preferred but non-limiting embodiments of the invention. In one form typical ingredients include fine granular premelted calcium alumino silicate, fine powder alumina/aluminium, a silica/carbon fine powder admixture, sodium silicate binder and calcium stearate lubricant. The ingredients are mixed together, and then compressed, ideally to a briquette form. Details of the ingredients are as follows, with a suitable composition range for the slag defoaming composite being listed in Example 1, whilst Example 2 provides an example of a typical specific composition. EXAMPLE 1 COMPOSITION RANGE FOR ONE FORM w/w Calcium Alumino Silicate 10-50% Alumina/Aluminium admixture 10-50% (5-60% Al) Silica/Carbon admixture 10-50% (3-15% C) Sodium silicate 0-20% Calcium stearate lubricant 0-2% EXAMPLE 2 COMPOSITION (TYPICAL BRIQUETTE FORMULATION) w/w Calcium Alumino Silicate 22.7 (adjusts the density) Alumina/Aluminium admixture 45 (14% Al) Fine Silica/Carbon admixture 22.7 (6.8% Carbon) (15.9% Si0 2 ) Sodium silicate 9.5% Calcium stearate lubricant 0.2kg/150kg mix 0.133- The calcium alumino silicate, or like material has a very important role in the manufacturing of the briquette. It is a non-absorbent/inert material which coarsens the mix and thus adjusts the particle size distribution which allows for the briquetting of the mixture. The binder material is important to bind the various components together. A silicate, such as sodium silicate or other similar silicate may be used, or alternatively, materials such as clay or lime, which have a binding effect may be used. Depending, however, on the other components of the composite, a specialised binder material may not need to be added. That is, the other components of the composite may have a binding effect on the ingredients of the composite, such that a specialised binder material is unnecessary. Various methods may be used to manufacture a suitable briquette - an example of which is now described. The ingredients such as calcium alumino silicate, alumina/aluminium and the carbon silica mixture are firstly weighed separately and added into a mixing mill. They are dry mixed typically for three to five minutes. Sodium silicate, which acts as a binder, is finely sprayed into the mix while the mill is blending and this proceeds for a further six to eight minutes. In the last one minute of mixing, the calcium stearate lubricant is added and mixed in. The long mixing time yields a relatively dry mix characterised by good flowability which is essential in the manufacturing process. It is important when blending the mix that it should be able to flow well, otherwise the size and density of the briquette may be difficult to control. The mixture should also be free of lumps. Optionally, slag fluidiser, cellulose based raw materials and flame retardents may also be included. In an optional embodiment of the invention, the composite may contain carbon in the range of 3 to 50% w/w. s ag fluidiser in the range of 0 to 30% w/w, and cellulose based raw materials, such as wood chips in the range of 3 to 30%. When the composite contains cellulose, flame retardent is added to prevent auto combustion in the hopper above the BOF. The mixture is then formed into a briquette. A preferred method of forming the briquette is to place the low moisture mixture in a hydraulic press and then to compress it to a pressure in excess of 20 tonnes per square inch to form a hard briquette with compression strength above 1000 kPa. A typical size for cylindrically shaped briquettes may be in the range of 65-75 mm in diameter and a 35-50mm in height. The typical density for the briquette in Example 2 would be in the vicinity of 2.4 g/cc; however densities in the range of 1.0 to 2.6 are quite acceptable. The density can generally be adjusted by varying the quantity of the dense inert granular material, eg., calcium alumino silicate present, the content of cellulose based-material or other variations in composition or processing. The briquettes are manufactured with different densities to suit different needs. For example, for steels with very viscous slag, briquettes of high density are required. Also the defoaming composite could be in various briquette shapes and sizes as well as in pellet and other forms. For example, the shape could be cylindrical, half cylindrical, rectangular, certain shapes being more preferable for transportation purposes, etc., as will be understood to persons skilled in the art. The slag defoaming composite as described herein has the advantage that the density of a slag defoaming composite - 1 - briquette can be chosen so as to penetrate the surface of the slag, but not sink into the steel. Being suspended within the slag layer results in an efficient exothermic reaction therefore improving the release of gases and reduction of slag viscosity which is desired in order to achieve defoaming. As mentioned this.typical density range is in the vicinity of 1.0 to 2.6 g/cc. Variation in the reactivity of the composite is controllable by variation in the composition thereof. Also, the very fine division of the ingredients used causes good dispersion of reactive elements and thus promotes a highly exothermic reaction to thin the slag. The size, shape and hardness of the briquettes allows them to be handled and placed into hoppers which are held above the basic oxygen furnace without breakage, and to freefall into the furnace without loss of product or thermal reaction, before penetrating the slag. A final important advantage of the slag defoaming composite is that it will not combust when stored in a hopper above the basic oxygen furnace and nor will it react exothermically with powdered lime which may enter into the hopper containing the composite. As will be appreciated by persons skilled in the art, numerous variations and modifications will become apparent to the specific embodiments hereinbefore described with reference to the examples. All such variations and modifications should be considered to fall within the scope of the invention as hereinbefore described and as hereinafter claimed.

Claims: THE CLAIMS : 1. A slag defoaming composite, comprising: a carbon source; a source of exothermic material, such as aluminium; a dense insert granular material, such as calcium alumina silicate; and a binder, optionally provided; characterised in that, said composite is selected to have a density sufficient to penetrate the slag layer during processing. 2. A slag defoaming composite as claimed in claim 1, wherein said composite is manufactured in the form of briquettes, pellets, and/or the like. 3. A slag defoaming composite as claimed in any one of claims 1 to 2, wherein said composite is substantially non-combustible. 4. A slag defoaming composite as claimed in any one of claims 1 to 3, wherein said density of said composite is selected to be in the range of 1.0 to 2.6 g/cc. 5. A slag defoaming composite as claimed in any one of claims 1 to 4, comprising: a carbon source which yields a carbon content of the composite within the range of 3 to 50% w/w; a source of exothermic material such as aluminium which yields aluminium content of the composite within the range of 5 to 60% w/w; a dense inert granular material within the range of 10 to 50% w/w; and a binder optionally provided within the range of 0 to 20% w/w. 6. A slag defoaming composite as claimed in claim 5, wherein said binder is sodium silicate, or a similar silicate binder be it organic or inorganic, or clay, lime, or the like. 7. A slag defoaming composite as claimed in any one of claims 1 to 6, further comprising a lubricant material. 8. A slag defoaming composite as claimed in claim 7, wherein said lubricant material is a stearate, such as calcium stearate. 9. A slag defoaming composite as claimed in claims 7 or 8, wherein said lubricant material is provided with the range of 0 to 2% w/w. 10. A slag defoaming composite as claimed in any one of claims 1 to 9, further comprising slag fluidiser. 11. A slag defoaming composite as claimed in claim 10, wherein said slag fluidiser is provided in the range of 0 to 30% w/w. 12. A slag defoaming composite as claimed in any one of claims 1 to 11, further comprising: cellulose based raw material; and flame retardent. 13. A slag defoaming composite as claimed in claim 12, wherein said cellulose based raw material is provided in the range of 3 to 30% w/w. 14. A slag defoaming composite, substantially as herein described. 15. A method of manufacturing/using a slag defoaming composite, substantially as herein described.

Inventors: MARIC MILENA, PYE ERIC, MARIC, MILENA, PYE, ERIC
Applicants: LAPORTE GROUP AUSTRALIA, MARIC MILENA, PYE ERIC, LAPORTE GROUP AUSTRALIA LIMITED, MARIC, MILENA, PYE, ERIC
Application year: 1994
Main classification: C21C5
IPC codes: C21C5